Multiple layer substrate support and exhaust gas treatment device

ABSTRACT

A mat or mat-pre-form hybrid for use in an exhaust gas treatment device, such as catalytic converters and diesel particulate traps that are used in automotive exhaust systems. The mat or hybrid may be used as a mounting mat to mount a fragile monolith within an outer housing of an exhaust gas treatment device or as thermal insulation in an end cone of the exhaust gas treatment device.

This application claims the benefit of the filing date, under 35 U.S.C.§119(e), of U.S. Provisional Application for Patent Ser. No. 61/234,003,filed on Aug. 14, 2009, and is a continuation-in-part of U.S. Ser. No.12/200,083, filed on Aug. 28, 2008, now U.S. Pat. No. 8,017,085 whichclaims priority from U.S. Provisional Application for Patent Ser. No.60/967,177, filed on Aug. 31, 2007, which applications are incorporatedherein by reference.

Disclosed is a mat or mat-pre-form hybrid for use in an exhaust gastreatment device, such as catalytic converters and diesel particulatetraps that are used in automotive exhaust systems. The mat or pre-formmay be used as a mounting mat to mount a fragile monolith within anouter housing of an exhaust gas treatment device or as thermalinsulation in an end cone of the exhaust gas treatment device.

Exhaust gas treatment devices are used on automobiles to reduceatmospheric pollution from engine emissions. Examples of widely usedexhaust gas treatment devices include catalytic converters and dieselparticulate traps, selective catalyst reduction units, NO_(x) traps, andthe like.

A catalytic converter for treating exhaust gases of an automotive engineincludes a housing, a fragile catalyst support structure or substratefor holding the catalyst that is used to effect the oxidation of carbonmonoxide and hydrocarbons and the reduction of oxides of nitrogen, and amounting mat disposed between the outer surface of the fragile catalystsupport structure and the inner surface of the housing to resilientlyhold the fragile catalyst support structure within the housing.

A diesel particulate trap for controlling pollution generated by dieselengines generally includes a housing, a fragile particulate filter ortrap for collecting particulate from the diesel engine emissions, and amounting mat that is disposed between the outer surface of the filter ortrap and the inner surface of the housing to resiliently hold thefragile filter or trap structure within the housing.

The materials comprising fragile catalyst support structures orsubstrates are commonly frangible or brittle materials exhibiting a highheat resistance, a low thermal expansion coefficient, and a low impactresistance. The fragile catalyst support structure typically comprises amonolithic structure manufactured from a frangible material of metal ora brittle, ceramic material such as aluminum oxide, silicon dioxide,magnesium oxide, zirconia, cordierite, silicon carbide and the like.These materials provide a skeleton type of structure with a plurality ofgas flow channels. These monolithic structures can be so fragile thateven small shock loads or stresses are often sufficient to crack orcrush them. In order to protect the fragile structure from thermal andmechanical shock and other stresses noted above, as well as to providethermal insulation and a gas seal, a mounting mat is positioned withinthe gap between the fragile structure and the housing.

The geometry comprising substrates typically promotes a high surfacearea to volume ratio. In certain embodiments, the substrate geometrycomprises a plurality of elements which are thin and fragile. Withoutlimitation, a common geometry for substrates is a monolith comprising anarray of hollow rectangular prism cells defining tiny flow channels,separated by thin, fragile walls, such as in a honeycomb-typeconfiguration.

Together, the geometric and material considerations for substratescommonly result in a substrate which is susceptible to impact, crushing,or other mechanical failure from small shockloads or stress, and whichoperates at very high temperatures. To address the problem of thefragile nature of the substrate, it is common to protect the substratewithin a housing, typically a metallic housing, with a space or gapbetween the external surface of the substrate and the internal surfaceof the housing. In order to protect the substrate from thermal andmechanical shock and other stresses, as well as to provide thermalinsulation, it is known to position at least one sheet of mountingmaterial within the gap between the substrate and the housing.

Because exhaust gas treatment devices are designed to operate attemperatures substantially higher than ambient temperatures and aredesigned to cool to ambient temperatures when not operating, exhaust gastreatment devices are designed to undergo significant temperaturefluctuations. The mounting of the substrate is designed to protect thesubstrate over the entire range of temperatures to which the device isexposed; from ambient through operating temperatures. The temperaturefluctuations present a considerable challenge in designing the substratemounting system.

A common means of mounting the substrate comprises inclusion of aninsulating mounting mat between the substrate and the metallic housing.The mounting mat may be wrapped about the substrate and may becompressed by enclosing the housing around it. The level of compressionis selected to provide an engagement force between the housing and themat; and, the mat and the substrate, which produces mounting or holdingforces both sufficiently high to secure the substrate with respect tothe housing, and sufficiently low to avoid damage to the substrate.Also, a mounting mat will inherently have some resistance to heat flowand, in certain embodiments is a good insulator; the mat resistspropagation of heat from the substrate to the housing and thereby lowersthe steady state operating temperature of the housing for a given steadystate operating temperature of the substrate.

Selection of a type of mounting material and the ambient temperaturecompression load to which to subject the mounting material to yieldacceptable mounting or holding forces at all temperatures that theexhaust gas treatment device experiences continues to be a source ofdifficulty. Compounding this difficulty is the need for an insulativematerial between the substrate and the housing having a low thermalconductivity but which will not add undesirable weight or bulk to thedevice.

DESCRIPTION

Disclosed is a multiple layer mat comprising a first layer comprising anon-intumescent sheet of inorganic fibers having a first major surfaceand a second major surface opposite the first major surface; a secondlayer comprising a non-intumescent sheet of inorganic fibers having afirst major surface and a second major surface opposite the first majorsurface; a microporous inorganic insulating layer positioned betweensaid first non-intumescent layer and second non-intumescent layer.

Also disclosed is an exhaust gas treatment device comprising a housing;a fragile structure located within the housing; and a multiple layermounting mat disposed between said housing and said fragile structure,said mat comprising a first layer comprising a non-intumescent sheet ofinorganic fibers having a first major surface and a second major surfaceopposite the first major surface; a second layer comprising anon-intumescent sheet of inorganic fibers having a first major surfaceand a second major surface opposite the first major surface; and amicroporous inorganic insulating layer positioned between said firstnon-intumescent layer and second non-intumescent layer.

Additionally disclosed is a multiple layer mat comprising a first layercomprising an intumescent sheet of inorganic fibers having a first majorsurface and a second major surface opposite the first major surface; asecond layer comprising an intumescent sheet of inorganic fibers havinga first major surface and a second major surface opposite the firstmajor surface; a microporous inorganic insulating layer positionedbetween the first intumescent layer and second intumescent layer.

Additionally disclosed is an exhaust gas treatment device comprising ahousing; a fragile structure located within the housing; and a multiplelayer mounting mat disposed between said housing and said fragilestructure, said mat comprising a first layer comprising an intumescentsheet of inorganic fibers having a first major surface and a secondmajor surface opposite the first major surface; a second layercomprising an intumescent sheet of inorganic fibers having a first majorsurface and a second major surface opposite the first major surface; anda microporous inorganic insulating layer positioned between the firstintumescent layer and second intumescent layer.

Additionally disclosed is a multiple layer mat comprising a first layercomprising a non-intumescent or intumescent sheet of inorganic fibershaving a first major surface and a second major surface opposite thefirst major surface; a second layer comprising a microporous inorganicinsulating layer having a first major surface and a second major surfaceopposite the first major surface; and a bonding means between said firstlayer and said second layer.

Additionally disclosed is an exhaust gas treatment device comprising ahousing; a fragile structure located within the housing; and a multiplelayer mounting mat disposed between said housing and said fragilestructure, said mat comprising a first layer comprising anon-intumescent or intumescent sheet of inorganic fibers having a firstmajor surface and a second major surface opposite the first majorsurface; a second layer comprising a microporous inorganic insulatinglayer having a first major surface and a second major surface oppositethe first major surface; and a bonding means between said first layerand said second layer.

Further disclosed is a multiple layer mat comprising a first layercomprising an intumescent or non-intumescent sheet of inorganic fibershaving a first major surface and a second major surface opposite thefirst major surface; a second layer comprising a microporous inorganicinsulating layer having a first major surface and a second major surfaceopposite the first major surface; and a banding means encircling atleast a portion of the exterior surfaces of said first layer and saidsecond layer.

Additionally disclosed is an exhaust gas treatment device comprising ahousing; a fragile structure located within the housing; and a multiplelayer mounting mat disposed between said housing and said fragilestructure, said multiple layer mat comprising a first layer comprising anon-intumescent or intumescent sheet of inorganic fibers having a firstmajor surface and a second major surface opposite the first majorsurface; a second layer comprising a microporous inorganic insulatinglayer having a first major surface and a second major surface oppositethe first major surface; and a banding means encircling at least aportion the exterior surfaces of said first layer and said second layer.

Further disclosed is a multiple layer mat comprising a first layercomprising a non-intumescent or intumescent sheet of inorganic fibers,said layer having a first major surface and a second major surfaceopposite the first major surface; a second layer adjacent said firstlayer, said second layer comprising a microporous inorganic insulatinglayer having a first major surface and a second major surface oppositethe first major surface; and wherein said first layer and second layerare encapsulated within a polymeric bag.

Additionally disclosed is an exhaust gas treatment device comprising ahousing; a fragile structure located within the housing; and a multiplelayer mounting mat disposed between said housing and said fragilestructure, said multiple layer mat comprising a first layer comprising anon-intumescent or intumescent sheet of inorganic fibers, said layerhaving a first major surface and a second major surface opposite thefirst major surface; a second layer adjacent said first layer, saidsecond layer comprising a microporous inorganic insulating layer havinga first major surface and a second major surface opposite the firstmajor surface; and wherein said first layer and second layer areencapsulated within a polymeric bag.

Further disclosed is a multiple layer mat comprising a first layercomprising a non-intumescent or intumescent sheet of inorganic fibershaving a first major surface and a second major surface opposite thefirst major surface; a second layer comprising a microporous inorganicinsulating layer; and a binder disposed between said first layer andsaid second layer.

Additionally disclosed is an exhaust gas treatment device comprising ahousing; a fragile structure located within the housing; and a multiplelayer mounting mat disposed between said housing and said fragilestructure, said multiple layer mat comprising a first layer comprising anon-intumescent or intumescent sheet of inorganic fibers having a firstmajor surface and a second major surface opposite the first majorsurface; a second layer comprising a microporous inorganic insulatinglayer; and a binder disposed between said first layer and said secondlayer.

Further disclosed is a multiple layer mat comprising a first layercomprising an intumescent or non-intumescent sheet of inorganic fibershaving a first major surface and a second major surface opposite thefirst major surface; a scrim layer having a first major surface and asecond major surface opposite the first major surface; and a microporousinorganic insulating layer positioned between the first layer and saidscrim layer.

Additionally disclosed is an exhaust gas treatment device comprising ahousing; a fragile structure located within the housing; and a multiplelayer mounting mat disposed between said housing and said fragilestructure, said multiple layer mat comprising a first layer comprisingan intumescent or non-intumescent sheet of inorganic fibers having afirst major surface and a second major surface opposite the first majorsurface; a scrim layer having a first major surface and a second majorsurface opposite the first major surface; and a microporous inorganicinsulating layer positioned between the first layer and said scrimlayer.

Further disclosed is a multiple layer support comprising a microporousinorganic insulating layer comprising a three-dimensional pre-form; anda flexible layer wrapped about at least a portion of the perimeter ofsaid pre-form.

Additionally disclosed is an exhaust gas treatment device comprising ahousing; a fragile structure located within the housing; and a multiplelayer support disposed between said housing and said fragile structure,said support comprising a microporous inorganic insulating layercomprising a three-dimensional pre-form; and a flexible layer wrappedabout at least a portion of the perimeter of said pre-form.

Further disclosed is a multiple layer support comprising athree-dimensional pre-form comprising an inner layer of microporousinorganic insulating material and an outer layer applied over at least aportion of said inner layer.

Additionally disclosed is an exhaust gas treatment device comprising ahousing; a fragile structure located within the housing; and a multiplelayer support disposed between said housing and said fragile structure,said support comprising a three-dimensional pre-form comprising an innerlayer of microporous inorganic insulating material and an outer layerapplied over at least a portion of said inner layer.

Further provided is a multiple layer mat comprising: a first layercomprising a non-intumescent sheet of inorganic fibers having a firstmajor surface and a second major surface opposite the first majorsurface; a second layer comprising an intumescent sheet of inorganicfibers having a first major surface and a second major surface oppositethe first major surface; and a microporous inorganic insulating layerpositioned between said first layer and second layer.

Additionally disclosed is a multiple layer mat comprising: a first layercomprising a sheet of inorganic fibers having a first major surface anda second major surface opposite the first major surface; a second layercomprising a sheet of inorganic fibers having a first major surface anda second major surface opposite the first major surface; a microporousinorganic insulating layer positioned between the first layer and thesecond layer.

Further disclosed is a multiple layer mat comprising: a first layercomprising a sheet of inorganic fibers having a first major surface anda second major surface opposite the first major surface; a second layeradjacent said first layer, said second layer comprising a microporousinorganic insulating layer having a first major surface and a secondmajor surface opposite the first major surface; and wherein the firstlayer and the second layer are encapsulated within a polymeric bag.

Additionally disclosed is a multiple layer mat comprising: a first layercomprising a sheet of inorganic fibers having a first major surface anda second major surface opposite the first major surface; a second layercomprising a microporous inorganic insulating layer having a first majorsurface and a second major surface opposite the first major surface; andeither: (i) a bonding means between the first layer and the secondlayer; (ii) a banding means encircling at least a portion of theexterior surfaces of the first layer and the second layer, such that thefirst layer is engaged with the second layer; or (iii) a scrim layer,wherein the second major surface of the first layer is engaged with thefirst major surface of the second layer, and the scrim layer is engagedwith the second major surface of the second layer.

Additionally disclosed is a multiple layer support comprising: amicroporous inorganic insulating layer comprising a three-dimensionalpre-form; and a flexible layer disposed about at least a portion of theperimeter of the three-dimensional pre-form.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows an illustrative embodiment of a mounting mat for an exhaustgas treatment device.

FIG. 2 shows another illustrative embodiment of a mounting mat for anexhaust gas treatment device.

FIG. 3 shows a further illustrative embodiment of a mounting mat for anexhaust gas treatment device.

FIG. 4 shows a further illustrative embodiment of a mounting mat for anexhaust gas treatment device.

FIG. 5 shows an illustrative embodiment of a mounting mat for an exhaustgas treatment device.

FIG. 6 shows an illustrative embodiment of a mounting mat for an exhaustgas treatment device.

FIG. 7 shows an illustrative embodiment of a hybrid mat-preform for anexhaust gas treatment device.

FIG. 8 shows another illustrative embodiment of a hybrid mat-preform foran exhaust gas treatment device.

FIG. 9 shows an illustrative embodiment of an exhaust gas treatmentdevice incorporating a hybrid mounting mat.

Provided is a substrate mounting system for mounting a fragile substratewithin a housing of an exhaust gas treatment device. The substratemounting system includes a microporous insulation layer and at least asecond layer. The substrate mounting system is positioned between theexterior surfaces of a fragile catalyst support structure, such as afragile monolithic substrate, and the inner surfaces of the housing ofthe exhaust gas treatment device.

The insulative layer of the substrate mounting system promotes theinsulative character of the material between the substrate and thehousing and thereby decreases the steady state operating temperature ofthe housing and other materials external to the insulative layer for agiven steady state operating temperature of the substrate. In suchembodiments, the insulation reduces the thermal strain which thematerials external to the insulative layer undergo, mitigating changesin the mounting or holding forces to which the substrate is subjected.In some embodiments, the insulative layer insulates the mat from thesubstrate and thereby decreases the operating temperature of the mat fora given operating temperature of the substrate. In such embodiments, thethermal strain which the mat undergoes is reduced, reducing changes inthe mounting or holding forces to which the substrate is subjected. Inother embodiments, the insulative layer is positioned between the matand the housing and thereby decreases the surface temperature of thehousing for a given operating temperature of the substrate. In suchembodiments, the thermal strain which the housing undergoes is reduced,reducing changes in the mounting or holding forces to which thesubstrate is subjected.

The exhaust gas treatment device generally comprises a fragilesubstrate, a housing, and a mounting system comprising a multilayermounting mat including a microporous inorganic insulating layer.Optionally, the device may further comprise additional components.

A substrate is a component in an exhaust gas treatment device whichmodifies exhaust material. There are many kinds of exhaust gas treatmentdevices which may comprise a substrate. One type of exhaust gastreatment device is a catalytic converter; the active portion of acatalytic converter comprises a substrate coated or impregnated with acatalyst to promote oxidation of carbon monoxide and hydrocarbons andthe reduction of oxides of nitrogen, at least partially eliminatingundesired products of combustion in the exhaust stream.

Substrate monoliths are typically oval or round in cross-sectionalconfiguration, but other shapes are possible. The substrate is spacedfrom its housing by a gap width distance which will vary according tothe type and design of the device utilized, e.g., a catalytic converter,a diesel catalyst structure, or a diesel particulate trap. In someembodiments the gap can be at least about 0.05 inch (1.27 mm), and inother embodiments the gap can be up to one inch (25.4 mm) or more. Thisgap width may typically range from about 3mm to about 25 mm with a rangeof about 3 mm to about 8 mm being commercially common widths. Thesubstrate mounting system is disposed in this space to provide boththermal insulation to the external environment and mechanical support tothe ceramic monolith substrate, protecting the substrate from damage dueto mechanical shock.

A diesel particulate filter is another type of exhaust gas treatmentdevice. The active portion of a diesel particulate filter comprises asubstrate acting as a filter. A diesel particulate trap may include oneor more porous tubular or honeycomb-like structures (having channelsclosed at one end, however), which are mounted by a thermally resistantmaterial within a housing. Particulate is collected from exhaust gasesin the porous structure, typically until regenerated by a hightemperature burnout process.

Another type of exhaust gas treatment device is a selective catalystreduction unit; the active portion of a selective catalyst reductionunit comprises a substrate, coated with a catalyst to promote chemicalreduction and at least partial elimination of undesired products in theexhaust stream.

Another type of exhaust gas treatment device is a NO_(x) trap; theactive portion of a NO_(x) trap comprises a catalytic substratecomprising alkali or alkaline earth materials. The trap operates in acyclic manner; cycling between a “sorbtion” process and a “regeneration”process. During sorbtion the substrate intakes NO_(x) species and trapsthem on the surface of the catalytic substrate as nitrate species.During regeneration, a reducing material is introduced into the NO_(x)trap and the nitrate species are removed from the substrate and reducedto nitrogen.

Non-automotive applications for the subject mounting system include butare not limited to catalytic converters for chemical industry emission(exhaust) stacks.

In an exhaust gas treatment device, the substrate may operate attemperatures substantially above ambient temperature. Withoutlimitation, the operating temperature for certain embodiments of exhaustgas treatment devices is about 1000° C. Because of the substantiallyelevated temperatures at which it operates, the substrate typicallycomprises materials having excellent resistance to heat, i.e., a veryhigh melting point, and very low thermal expansion coefficient. Thereare many materials which have these properties including a wide varietyof ceramics, tungsten, rhenium, and more exotic materials. One group ofvery common materials which exhibit excellent resistance to heat isceramics. Exhaust gas treatment device substrates typically comprise aheat resistant frangible material, such as a monolithic structure formedof a brittle, fireproof ceramic material such as, but not limited to,aluminum oxide, silicon dioxide, magnesium oxide, zirconia, cordierite,silicon carbide and the like.

A property of many common ceramics is their low toughness. That is,while many ceramics are hard, strong, or both hard and strong, ceramicstend to display low toughness and tend to fracture at low strain levels.This makes ceramic components prone to breakage or fracture undermechanical loading conditions typically experienced by an exhaust gastreatment device. Therefore, it is common to incorporate means toprotect the substrate.

A housing is a hollow body which at least partially encloses thesubstrate. The housing protects the substrate from impact, torsion,tension, compression, or other mechanical loading which may damage thesubstrate. In certain embodiments. the housing comprises a thin shell.The housing comprises materials having good resistance to heat, i.e., ahigh melting point and high heat resistance. The materials comprisingexhaust gas treatment device housings are commonly ductile materialscomprising a lower heat resistance than the monolith, a higher thermalexpansion coefficient than the monolith, and a higher impact resistancethan the monolith. Without limitation, in certain embodiments theexhaust gas treatment device housing comprises a metal or metal alloy,such as high temperature-resistant steel.

The present substrate mounting system may comprise at least onemicroporous insulating layer, and at least one flexible, fibrous matwhich when combined, form a hybrid mounting system for incorporationwithin an exhaust gas treatment device. The insulating layer and thefibrous mat may be combined in a variety of ways to form the presentmounting system and a variety of techniques may be employed to achievesuch a combination.

According to certain embodiments, the mounting system may bepreassembled by combining the insulating layer and the second or morelayers to form a multiple layer unit. Various devices and methods may beutilized to hold the insulating layer and the layer(s) together.According to certain embodiments, the layers of the mounting mat may beconnected together through the use of an elongated banding means, suchas a tourniquet. The tourniquet material may comprise a tape, anon-adhesive tape or a film or a combination thereof. For example, insome embodiments, the majority of the tourniquet material may comprise anon-adhesive tape with the ends of the tourniquet material secured by anadhesive tape, while in other embodiments, the entire length of thetourniquet material may comprise an adhesive tape or elastic bands.

Another way of holding the layers of the mounting mat together isthrough the use of spot bonding. For example, in some embodiments, theinsulating layer may be spot bonded to the mounting mat. Typically,adhesive is applied in a spot-like manner to various areas on themounting mat. A film wrapped insulating layer is then applied over theadhesive treated side of the mounting mat. The fibrous mat andinsulating layer are then secured together by the application ofpressure to form a single unit for assembly within an exhaust gastreatment device.

Alternatively, a two-sided tape may be employed to attach the insulatinglayer and the fibrous mat together. In this embodiment, the two-sidedtape may be applied to either a film wrapped insulating layer or thefibrous mat. The film wrapped insulating layer is placed over the tapetreated side of the fibrous mat or the fibrous mat is placed over thetape treated side of the film wrapped insulating layer. Applyingpressure to the insulating layer and the fibrous mat adheres bothcomponents to each other to secure and form a single unit for assemblywithin an exhaust gas treatment device.

In addition to spot bonding and two-sided tapes, other means for bondingthe insulating layer and the fibrous mat together include brush/rollapplication of an adhesive, applying a spray-on adhesive, or applying ahot melt to secure the two components together to form a single unit forassembly within an exhaust gas treatment device. Brush/roll adhesives,spray-on adhesives and hot melts may be applied to either a film wrappedinsulating layer or the fibrous mat followed by positioning thecomponents over one another, and securing the components togetherthrough the application of pressure in a manner similar to thatdescribed above.

In an alternative embodiment, the insulating layer and the fibrous matmay be encapsulated within a single polymeric bag. The encapsulationmaterial or bag may be formed from a polyethylene polymer that is shrinkwrapped or vacuum formedaround the insulating layer and the fibrous matto form a multiple layer unit for installation within an exhaust gastreatment device.

According to other embodiments, the mounting system comprising theinsulating layer and the fibrous mat may form a single unit through thecreation of a sandwich hybrid of the two components. A sandwich hybridtypically comprises an inner sandwich layer and an outer sandwich layer.According to certain embodiments, the sandwich hybrid of the presentdisclosure may comprise positioning an insulating layer (the innersandwich layer) between two flexible fibrous layers (the outer sandwichlayers) or positioning a flexible fibrous layer (as an inner sandwichlayer) between two insulating layers (the outer sandwich layers). Eithera single flexible fibrous layer and insulating layer may be used ordiffering types of flexible fibrous layers and insulating layers may beused to form the sandwich hybrid.

Also, the sandwich hybrid may comprise multiple inner sandwich layers,multiple outer sandwich layers, several sandwich hybrid layers, orseveral hybrid layers of multiple inner and/or outer sandwich layers. Inone such embodiment, the flexible fibrous layer and the insulating layerare held together by a scrim. The scrim functions as an outer sandwichlayer which holds the insulating layer to the flexible fibrous layer.The insulating layer may or may not need to be encapsulated by a filmdepending upon its position within the mounting system. For example, theporosity of the scrim may necessitate the encapsulation of theinsulating layer when the insulating layer is positioned between theflexible fibrous layer and the scrim. Positioning the insulating layerbetween two layers of flexible fibrous layer may not necessitate theencapsulation of the insulating layer due to the low porosity typicallyexhibited by flexible fibrous layers. Various types of scrims may beused including tea bags, aluminum foil, ethylene, and Isofrax paper(commercially available fibers from Unifrax I LLC, Niagara Falls, N.Y.,under the trademark ISOFRAX®). In addition to the scrim, an adhesive maybe used to aid in the formation of the multiple layer mounting system.This adhesive may be a polymer present within the flexible fibrous layeror within the scrim.

An alternative embodiment of the sandwich hybrid utilizes heat andpressure to bind or weld the flexible fibrous layer(s) and theinsulating layer together. In one such embodiment, the insulating layeris positioned between two flexible fibrous layers. The positioning ofthe insulating layer between two flexible fibrous layers renders theinsulating layer not visible from an exterior view of the mountingsystem. The insulating layer may or may not be encapsulated within ashrink wrap or wrapped within a film. An example of one such embodimentincludes an insulating layer of Wacker WDS® 1000 from Wacker Chemie GmbH(Munich) sandwiched between two layers of low basis weight mounting mat,such as ISOMAX® AV1 available from Unifrax I LLC, Niagara Falls, N.Y.

A further alternative embodiment of the sandwich hybrid mounting systemcomprises application of a binder spray to adhere the insulating layerto and between two flexible fibrous layers. The binder spray functionsas an adhesive and is applied on the surfaces of the insulating layerand flexible fibrous layer as necessary to secure an adequate adhesionof the individual components to form a single unit mounting system forinstallation within an exhaust gas treatment device.

In an alternative embodiment, the mounting system comprises a preformedcylinder comprising an inner layer and an outer layer that can beassembled within an exhaust gas treatment device as a single unit. Onesuch embodiment comprises an insulating layer that is preformed as acylinder and at least one flexible fibrous layer wrapped around theinsulating layer. In this embodiment, the insulating layer is pressedinto the shape of a cylinder to form the inner layer of the preformedcylinder. At least one flexible fibrous layer is then wrapped around thecylinder of insulative material forming the outer layer of the preformedcylinder. The cylindrical shape of the mounting system in thisembodiment allows the mounting system to be slide wrapped over thesubstrate of an exhaust gas treatment device where desired.

Another embodiment of the preformed cylinder mounting system comprisespreforming the insulative and the fibrous material layer together into acylindrical shape as a single unit without having to separately wrap themounting mat around the cylindrical insulating layer. The resultingpreformed cylinder comprises two separate and distinct layers ofinsulative and fibrous mat material wherein the inner cylindrical layercomprises the insulative material and the outer cylindrical layercomprises the flexible fibrous material.

The insulating layer as described above is a layer of materialcharacterized by a low thermal conductivity. As with any other designprocess, during design of an exhaust gas treatment device,considerations of weight savings and space savings must be balancedagainst cost considerations. Materials which exhibit low density or lowbulk and take up little space, are desirable. In certain embodiments,the insulating layer exhibits both low density and low bulk. In certainembodiments, the stiffness of the insulating layer is between 3 MPa and5 MPa for strains less than 0.1. For example, at strains less than 0.1,the insulating layer WDS® Flexible Contour (from Porextherm GmbH ofKempten, Germany) has a modulus of approximately 4 MPa, compared to themounting mat alone having a modulus approaching zero (0) and thecombined mounting system also having a modulus approaching zero (0).

Mounting support systems provide engagement forces which are developedby compression of the materials comprising the support system. Whilemany materials are compressible, only materials which are compressibleand are substantially elastic can return the energy thereby imparted tothem to the system as an engagement force. Non-stiff materials willundergo large strains at low stresses and incorporate the energy causingthe strain, the strain energy. Non-stiff, substantially elasticmaterials, will undergo large strains at low stresses, incorporate thestrain energy, and return a substantial portion of the strain energy asa restoring force. This restoring force contributes to the mounting orholding force. Stiff materials will undergo small strains, at lowstresses and incorporate the strain energy. Stiff, substantially elasticmaterials, will undergo small strains at low stresses, incorporate thestrain energy, and return a substantial portion of the strain energy asa restoring force.

A subject mounting system incorporates one or more layers of material,all mechanically loaded at once such that all layers experiencesubstantially identical stress. This kind of loading is “seriesloading”. In series loading, non-stiff layers will undergo greaterstrain and therefore incorporate greater strain energy than will thestiffer layers. Because there is a positive correlation between theamount of strain energy incorporated into a material during a givenloading cycle and the hysteretic erosion of the material, stiffermaterials may be protected from certain kinds of erosion byincorporating them in series with a non-stiff material. In certainembodiments a stiff insulating layer (relative to the mounting mat) isincorporated into the mounting system in series with a non-stiffmounting mat.

The insulating layer may include at least material from a class ofmaterials available as thin, somewhat flexible sheets which exhibit lowthermal conductivity and are substantially non-intumescent. According tocertain embodiments, the insulating layer is a microporous inorganicinsulation layer comprising a thin, flexible sheet exhibiting extremelylow thermal conductivity.

Such microporous inorganic insulation is available as thin, flexiblesheets having a thermal conductivity at 20° C. and at a density of about350 kg/m³ of less than about 0.021 W/mK. In certain embodiments theinsulating layer is a microporous insulation comprising a thin, flexiblesheet exhibiting a thermal conductivity at 20° C. and at about 350 kg/m³of less than about 0.021 W/mK, and having a thermal conductivity lessthan 0.055 W/mK for temperatures less than about 1000° C.

In certain embodiments, the insulating layer is a microporous inorganicinsulation comprising a thin, flexible sheet exhibiting a thermalconductivity at 20° C. and at a density of about 350 kg/m³ of less thanabout 0.021 W/mK, and a thermal conductivity less than 0.055 W/mK fortemperatures less than 1000° C., having a bulk density between about 260kg/m³ and about 520 kg/m³. Microporous inorganic insulation having agreater density may be acceptable if sufficiently flexible to wraparound and conform to the outer surface of the substrate. In certainembodiments the insulating layer having these properties is available asthin, flexible sheets having a thickness between about 3 mm and about 20mm.

In certain embodiments the insulating layer is substantiallyincompressible. One type of microporous inorganic insulation exhibitsthe compression performance shown in TABLE I at a density of about 350kg/m³. In TABLE I, the listed pressures are those required to compressthe material by the listed percentages at the listed temperatures.

TABLE I Compression 20° C. 400° C. 800° C. 1% 0.034 MPa 0.028 MPa 0.028MPa 3% 0.089 MPa 0.083 MPa 0.110 MPa 5% 0.151 MPa 0.144 MPa 0.165 MPa10%  0.275 MPa 0.295 MPa 0.350 MPa

The microporous inorganic insulating layer comprises finely dividedmetal oxide and an opacifier, that is, a material that minimizesinfra-red radiation; and optionally further comprises reinforcinginorganic fiber, such as glass filaments. The inorganic insulatinglayer, in its pre-installed form, may be sealed in a polymeric film,such as polyethylene, although the film may be selected for economy andfunctionality rather than composition. It is also possible that a minoramount of organic fibers or particles may be incorporated into themicroporous insulating layer for processing considerations.

The finely divided metal oxide may comprise at least one of pyrogenicsilicas, arc silicas, low-alkali precipitated silicas, silicon dioxideaerogels, aluminum oxides similarly prepared, and mixtures thereof. Inone embodiment, the finely divided metal oxide comprises fumed silica.The finely divided metal oxide may have a specific BET surface area offrom about 50 to about 700 m²/g, in particular from about 70 to about400 m²/g.

The particle sizes of the materials in the microporous insulating layerare small enough that mechanisms of heat transfer are controlled. Theparticulate and fibrous material are sized to create pores which areless than about 0.1 microns in diameter, less than the mean free path ofair. By limiting the quantity and motion of air in the pores, bothconduction due to air and convection heat transfer is limited, thusreducing thermal conductivity.

The opacifier may comprise at least one of ilmenite, titanium dioxide,iron(II)/iron(III) mixed oxides, chromium dioxide, zirconium oxide,manganese dioxide, iron oxide, rutile, zirconium silicate, siliconcarbide, and mixtures thereof. The opacifier may have a particle sizeless than about 15 microns, in certain embodiments, in the range fromabout 0.1 to about 10 microns.

The reinforcing fiber of the insulation layer may comprise a broadfamily of materials. The family of materials includes any inorganicfiber capable of providing the structure necessary to retain themicroporous particles in a cohesive unit. The reinforcing fiber may beselected from aluminum silicate, magnesium silicate, rockwool, orcombinations thereof. In certain embodiments, reinforcing fiber of theinsulation layer may comprise at least one of textile glass fibers orquartz fibers, such as high-temperature-resistant fibers having an SiO₂content of greater than 60% by weight, and in some embodiments greaterthan 90% by weight, silica fibers, textile fibers made from R glass,textile fibers made from S2 glass, textile fibers made from ECR glass,and fibers made from aluminum silicate. The fiber diameter may begreater than about 1.5 microns.

An insulating sheet commercially available from Porextherm GmbH(Kempten, Germany), comprises 55 weight % of HDK N25 highly dispersedsilica (BET 280 m2/g), 40 weight % of zirconium silicate, 5 weight % oftextile glass fibers (silicon content>92%) having a density of 320 kg/m3and a thickness of 10 mm. This sheet is substantially incompressible.

Another such microporous inorganic insulating material is WDS® FlexibleContour insulation, available from Porextherm GmbH (Kempten, Germany).WDS® Flexible Contour microporous insulation (WDS) is an exemplativematerial comprising about 50% silica, about 45% zirconium silicate, andabout 5% of other materials, including reinforcing glass fibers, whichmay be used as an insulating layer that exhibits the low thermalconductivity discussed above in a low density, thin material. Withoutlimitation, WDS® Flexible Contour is commercially produced in 3 mm, 5mm, 7 mm, 10 mm, and 20 mm thicknesses. Similar microporous insulationmaterial is available from Microtherm (Alcoa, Tenn.).

The microporous inorganic insulating layer engages the substrate eitherdirectly, or indirectly through an intermediate component, such as butnot limited to, the flexible fibrous layer. The insulating layer isinstalled into the exhaust gas treatment device between the housing andthe substrate. Placement of the insulating layer amongst othercomponents of the exhaust gas treatment device determines whichcomponents are on the substrate side (hot side) of the insulating layerand which components are on the housing side (cold side) of theinsulating layer.

An inorganic fibrous support or mounting mat is a substantially elastic,compressible material layer. The mounting mat is subject to heating bythe substrate, and at least indirectly by the exhaust gases, andtherefore may also operate at temperatures above ambient temperatures. Asupport or mounting mat typically comprises materials able to withstandelevated temperature environments while remaining substantially elasticand compressible. Fibrous mounting mats may comprise materials rangingfrom relatively inexpensive materials such as, for example, amorphousglass fibers such as S-glass, to more expensive materials such as, forexample, high alumina ceramic oxide fibers. Intumescent materials aswell as non-intumescent materials have been and continue to be employedin mounting mats, depending upon the application and conditions underwhich the mounting mats are to be used.

The fibrous mounting mat engages the substrate, either indirectlythrough an intermediate component or directly, and substantiallyimmobilizes it with respect to the housing. At least one fibrousmounting mat is disposed in the exhaust gas treatment device between thehousing and the substrate. The installed fibrous mounting mat iscompressed such that it imparts a load, either indirectly through anintermediate component, or directly, on the housing and the substrate.As noted above, the amount of the compressive load is substantiallyproportional to the amount of compression. A friction force resultingfrom the normal force is also substantially proportional to the amountof compression. These forces, the compression force and the frictionforce, together or separately, substantially immobilize the substratewith respect to the housing. By “substantially immobilize” it is meantthat the amount that the substrate may move with respect to the housingis very small, on the order of the largest elastic strain limit of thematerials providing holding forces. In certain embodiments, the largestelastic strain limit of the materials providing holding forces is about1% of the material thickness.

The flexible fibrous material refers to at least one sheet or layerprimarily comprising high temperature resistant fiber, such as but notlimited to ceramic fiber, and optionally including either within said atleast one sheet or layer, or in an additional sheet or layer,intumescent material, reinforcing material, and the like. The hightemperature resistant fiber, or ceramic fiber, sheet or layer may be invarious forms such as paper, blanket, mat or felt, provided such formimparts the necessary thermal insulation and mechanical support.

In certain embodiments, the fibrous mounting mat may comprise Fiberfrax®paper available from Unifrax I LLC, Niagara Falls, N.Y. This product ismade from bulk alumino-silicate glassy fiber having approximately 50/50alumina/silica and a 70/30 fiber/shot ratio. About 93 weight percent ofthis paper product is ceramic fiber/shot, the remaining 7 percent beingin the form of an organic latex binder. For higher substrate monolithtemperatures, papers produced from Fibermax® polycrystalline mulliteceramic fibers available from Unifrax or alumina fibers may be employed.Other ceramic fibers that may be used include those formed from basalt,industrial smelting slags, alumina, zirconia, zirconia-silicates,alumino-silicates and chrome, zircon and calcium modifiedalumino-silicates and the like.

The flexible fibrous material layer may include an intumescent agent ormaterial. The intumescent material may include at least one ofunexpanded vermiculite, hydrobiotite, water-swelling tetrasilicicfluorine mica, alkaline metal silicates, or expandable graphite, and maybe formed into a sheet using organic and/or inorganic binders to providea desirable degree of wet strength. A sheet of intumescent material canbe produced by standard paper making techniques as described, forexample, in U.S. Pat. No. 3,458,329, the disclosure of which isincorporated herein by reference.

The flexible fibrous material layer may be produced in several differentways, including a conventional paper-making process, either hand laid ormachine laid. A handsheet mold, a Fourdrinier paper machine, or arotoformer paper machine can be employed to make the flexible,intumescent fibrous mounting mat. In any case, a flocculated aqueousslurry containing a number of components, as set forth below, is pressedto remove most of the water, and the mat is then dried. This process iswell known to those skilled in the art.

In other embodiments, the flexible, fibrous mounting mat may comprise asubstantially non-expanding composite sheet of high temperatureresistant fibers and a binder. In certain embodiments, the mounting matis “integral”, meaning that after manufacture the mounting mat has selfsupporting structure, needing no reinforcing or containment layers offabric, plastic or paper, (including those which are stitch-bonded tothe mat) and can be handled or manipulated without disintegration. By“substantially non-expanding” is meant that the sheet does not readilyexpand upon the application of heat as would be expected withintumescent paper. Of course, some expansion of the sheet does occurbased upon its thermal coefficient of expansion. The amount ofexpansion, however, is insubstantial as compared to the expansion whichoccurs based upon intumescent properties. It will be appreciated thatthis type of mounting mat is substantially devoid of intumescentmaterials.

High temperature resistant fiber, including ceramic fibers which areuseful in the non-expanding mounting mat include polycrystalline oxideceramic fibers such as mullite, alumina, high alumina aluminosilicates,aluminosilicates, zirconia, titania, chromium oxide and the like. Incertain embodiments, the fibers are refractory. When the ceramic fiberis an aluminosilicate, the fiber may contain between about 55 to about98% alumina and between about 2 to about 45% silica, in certainembodiments with the ratio of alumina to silica being between 70 to 30and 75 to 25. Suitable polycrystalline oxide refractory ceramic fibersand methods for producing the same are contained in U.S. Pat. Nos.4,159,205 and 4,277,269, which are incorporated herein by reference.FIBERMAX® polycrystalline mullite ceramic fibers are available fromUnifrax I LLC, Niagara Falls, N.Y. in blanket, mat or paper form. Thefibers used in the non-expanding mounting mat may be substantially shotfree, having very low shot content, generally on the order of about 5percent nominally or less. The diameters of such fibers may be generallyabout 1 micron to about 10 microns.

The binder used in the non-expanding fibrous mounting mat is typicallyan organic binder which may be sacrificial in nature. By “sacrificial”is meant that the binder will eventually be burned out of the mountingmat, leaving only the fibers as the final mounting mat. Suitable bindersinclude aqueous and nonaqueous binders, but often the binder utilized isa reactive, thermally setting latex which after cure is a flexiblematerial that can be burned out of the installed mounting mat asindicated above. Examples of suitable binders or resins include, but arenot limited to, aqueous based latexes of acrylics, styrene-butadiene,vinylpyridine, acrylonitrile, vinyl chloride, polyurethane and the like.Other resins include low temperature, flexible thermosetting resins suchas unsaturated polyesters, epoxy resins and polyvinyl esters. Specificuseful binders include but are not limited to HI-STRETCH V-60™, atrademark of B.F. Goodrich Co. (Akron, Ohio) for acrylonitrile basedlatex. Solvents for the binders can include water, or a suitable organicsolvent, such as acetone, for the binder utilized. Solution strength ofthe binder in the solvent (if used) can be determined by conventionalmethods based on the binder loading desired and the workability of thebinder system (viscosity, solids content, etc.).

Similarly, the non-expanding mounting mat can be prepared byconventional papermaking techniques. Using this process, the inorganicfibers are mixed with a binder to form a mixture or slurry. The slurrymay then be diluted with water to enhance formation, and it may finallybe flocculated with flocculating agent and drainage retention aidchemicals. Then, the flocculated mixture or slurry may be placed onto apapermaking machine to be formed into a ceramic paper mat. The mats orsheets may be formed by vacuum casting the slurry or mixture withconventional papermaking equipment and are typically dried in ovens.

Alternatively, the fibers may be processed into a mat by conventionalmeans such as dry air laying. The mat at this stage, has very littlestructural integrity and is very thick relative to the conventionalcatalytic converter and diesel trap mounting mats. Where thisalternative technique is used, the mat may be further processed by theaddition of a binder to the mat by impregnation to form a discontinuousfiber composite. The binder is added after formation of the mat, ratherthan forming the mat prepreg as noted hereinabove with respect to theconventional papermaking technique.

In another embodiment, high index, crystallized, melt-formed refractoryceramic fibers are heat treated at temperatures above the mullitecrystallization temperature of 980° C., such as temperatures rangingfrom 990° C. to about 1400° C. in a controlled manner to obtain specificamounts of crystallinity and crystallite size, thereby increasing fiberperformance in the form of a catalytic converter mounting mat. Incertain embodiments, such fibers will have at least about 5 to about 50percent crystallinity as detected by x-ray diffraction, and acrystallite size of from about 50 Å to about 500 Å. When such fibers areemployed, the mounting mat provides a minimum pressure for holding thefragile catalyst support structure within the housing across a wideoperating temperature range normally encountered by automotive exhaustgas treatment device applications. By way of example, but not inlimitation, such a mounting mat may provide a minimum holding pressureof at least one of i) at least 2 psi after at least 200 cycles and/orafter 1000° C. of testing at 900° C. or ii) at least about 5 psi afterat least 1000 cycles of testing at 750° C. The ceramic fibers which areuseful in this embodiment are melt-formed ceramic fibers containingalumina and silica, including but not limited to melt spun refractoryceramic fibers. These include aluminosilicates, such as thosealuminosilicate fibers having from about 40 to about 60 percent aluminaand from about 60 to about 40 percent silica, and some embodiments, fromabout 47 to about 53 percent alumina and from about 47 to about 53percent silica. The melt-formed, spun fibers are of high puritychemically and may have an average diameter in the range of about 1 toabout 14 μm, and in certain embodiments, in the range of about 3 to 6.5μm. The fibers are beneficiated as is well known in the art to obtain agreater than 90 percent fiber index, meaning they contain less than 10percent shot, and often only about 5 percent shot.

In yet another embodiment, a flexible, fibrous, non-intumescent mountingmat for a substrate in a low temperature exhaust gas treatment devicecomprises high temperature resistant, amorphous, inorganic fibers andoptionally includes a binder. The fibers may have a use temperature upto about 1260° C., a Young's Modulus of less than about 20×10⁶ psi, anda geometric mean diameter less than about 5 μm. The fibers may compriseat least one of an amorphous alumina/silica fiber, analumina/silica/magnesia fiber (such as S-2 Glass from Owens Corning,Toledo, Ohio), mineral wool, E-glass fiber, magnesia-silica fibers, suchas ISOFRAX® fibers from Unifrax I LLC, Niagara Falls, N.Y., orcalcia-magnesia-silica fibers, such as INSULFRAX® fibers from Unifrax ILLC, Niagara Falls, N.Y. or SUPERWOOL™ fibers from Thermal CeramicsCompany.

The alumina/silica fiber typically comprises from about 45% to about 60%Al₂O₃ and about 40% to about 55% SiO₂; and the fiber may comprise about50% Al₂O₃ and about 50% SiO₂. The alumina/silica/magnesia glass fibertypically comprises from about 64% to about 66% SiO₂, from about 24% toabout 25% Al₂O₃, and from about 9% to about 10% MgO. The E-glass fibertypically comprises from about 52% to about 56% SiO₂, from about 16% toabout 25% CaO, from about 12% to about 16% Al₂O₃, from about 5% to about10% B₂O₃, up to about 5% MgO, up to about 2% of sodium oxide andpotassium oxide and trace amounts of iron oxide and fluorides, with atypical composition of 55% SiO₂, 15% Al₂O₃, 7% B₂O₃, 3% MgO, 19% CaO andtraces of the above mentioned materials.

According to certain embodiments, the flexible fibrous material layercomprises a layer, ply or sheet of biosoluble inorganic fibers. The term“biosoluble”, with regard to inorganic fibers, refers to inorganicfibers that are soluble or otherwise decomposable in a physiologicalmedium or in a simulated physiological medium, such as simulated lungfluid. The solubility of the fibers may be evaluated by measuring thesolubility of the fibers in a simulated physiological medium over time.A method for measuring the biosolubility (i.e. the non-durability) ofthe fibers in physiological media is disclosed U.S. Pat. No. 5,874,375assigned to Unifrax I LLC, which is incorporated herein by reference.Other methods are suitable for evaluating the biosolubility of inorganicfibers. According to certain embodiments, the biosoluble fibers exhibita solubility of at least 30 ng/cm²-hr when exposed as a 0.1 g sample toa 0.3 ml/min flow of simulated lung fluid at 37° C. According to otherembodiments, the biosoluble inorganic fibers may exhibit a solubility ofat least 50 ng/cm²-hr, or at least 100 ng/cm²-hr, or at least 1000ng/cm²-hr when exposed as a 0.1 g sample to a 0.3 ml/min flow ofsimulated lung fluid at 37° C.

Without limitation, suitable examples of biosoluble inorganic fibersthat can be used to prepare a flexible fibrous material layer for anexhaust gas treatment device include those biosoluble inorganic fibersdisclosed in U.S. Pat. Nos. 6,953,757, 6,030,910, 6,025,288, 5,874,375,5,585,312, 5,332,699, 5,714,421, 7,259,118, 7,153,796, 6,861,381,5,955,389, 5,928,075, 5,821,183, and 5,811,360, each of which areincorporated herein by reference.

According to certain embodiments, the biosoluble alkaline earth silicatefibers may comprise the fiberization product of a mixture of oxides ofmagnesium and silica. These fibers are commonly referred to asmagnesium-silicate fibers. The magnesium-silicate fibers generallycomprise the fiberization product of about 60 to about 90 weight percentsilica, from greater than 0 to about 35 weight percent magnesia and 5weight percent or less impurities. According to certain embodiments, thealkaline earth silicate fibers comprise the fiberization product ofabout 65 to about 86 weight percent silica, about 14 to about 35 weightpercent magnesia, 0 to about 7 weight percent zirconia and 5 weightpercent or less impurities. According to other embodiments, the alkalineearth silicate fibers comprise the fiberization product of about 70 toabout 86 weight percent silica, about 14 to about 30 weight percentmagnesia, and 5 weight percent or less impurities. More information onmagnesia-silica fibers can be found in U.S. Pat. No. 5,874,375, which ishereby incorporated by reference.

A suitable magnesium-silicate fiber is commercially available fromUnifrax I LLC (Niagara Falls, N.Y.) under the registered trademarkISOFRAX. Commercially available ISOFRAX fibers generally comprise thefiberization product of about 70 to about 80 weight percent silica,about 18 to about 27 weight percent magnesia and 4 weight percent orless impurities.

According to certain embodiments, the biosoluble alkaline earth silicatefibers may comprise the fiberization product of a mixture of oxides ofcalcium, magnesium and silica. These fibers are commonly referred to ascalcia-magnesia-silicate fibers. According to certain embodiments, thecalcia-magnesia-silicate fibers comprise the fiberization product ofabout 45 to about 90 weight percent silica, from greater than 0 to about45 weight percent calcia, from greater than 0 to about 35 weight percentmagnesia, and 10 weight percent or less impurities. Typically,biosoluble calcia-magnesia-silica fibers comprise about 15% to about 35%CaO, about 2.5% to about 20% MgO, and about 60 to about 70% SiO₂.

Useful calcia-magnesia-silicate fibers are commercially available fromUnifrax I LLC (Niagara Falls, N.Y.) under the registered trademarkINSULFRAX. INSULFRAX fibers generally comprise the fiberization productof about 61 to about 67 weight percent silica, from about 27 to about 33weight percent calcia, and from about 2 to about 7 weight percentmagnesia. Other suitable calcia-magnesia-silicate fibers arecommercially available from Thermal Ceramics (Augusta, Ga.) under thetrade designations SUPERWOOL 607 and SUPERWOOL 607 MAX. SUPERWOOL 607fibers comprise about 60 to about 70 weight percent silica, from about25 to about 35 weight percent calcia, and from about 4 to about 7 weightpercent magnesia, and trace amounts of alumina. SUPERWOOL 607 MAX fiberscomprise about 60 to about 70 weight percent silica, from about 16 toabout 22 weight percent calcia, and from about 12 to about 19 weightpercent magnesia, and trace amounts of alumina.

The biosoluble fibers are typically amorphous inorganic or glass fibersthat may be melt-formed, are fibers of high chemical purity (greaterthan about 98%) and may have an average diameter in the range of about 1to about 10 μm, and in certain embodiments, in the range of about 2 to 4μm. While not specifically required, the fibers may be beneficiated, asis well known in the art.

Optionally, the non-intumescent flexible fibrous material layer includesa binder. Suitable binders include aqueous and non aqueous binders, butthe binder typically utilized is a reactive, thermally setting latexwhich after cure is a flexible material that is stable up to at leastabout 350° C. About 5 to about 10 percent latex may be employed.

According to illustrative embodiments, the flexible fibrous materiallayer may include at least 25, 50, 75, 85 or 95 weight percent of thebiosoluble inorganic fibers, based upon 100 percent of the totalflexible fibrous material layer weight. According to certainillustrative embodiments, the flexible fibrous material layer comprisesabout 25 to about 100 weight percent alkaline earth silicate fibers,based upon 100 weight percent of the total flexible fibrous materiallayer weight. The flexible fibrous material layer may alternativelycomprise about 50 to about 100 weight percent alkaline earth silicatefibers, based upon 100 weight percent of the total flexible fibrousmaterial layer weight. According to one embodiment, the mounting matcomprises about 66 weight percent alkaline earth silicate fibers, basedupon 100 weight percent of the total flexible fibrous material layerweight.

In certain embodiments, the flexible, fibrous material layer comprisesone or more non-intumescent plies of melt-formed, amorphous,high-temperature resistant leached glass fibers having a high silicacontent and, optionally, includes a binder or other fibers suitable foracting as a binder. By the term “high silica content,” it is meant thatthe fibers contain more silica than any other compositional ingredientin the fibers. In fact, the silica content of these fibers afterleaching are typically greater than any other glass fibers containingsilica, including S-glass fibers, except crystalline quartz derivedfibers or pure silica fibers. In one embodiment, it will be appreciatedthat the mounting mat may be devoid of intumescent materials, solgel-derived glass silica fibers and/or backing or reinforcing layers.

Generally, the leached glass fibers will have a silica content of atleast 67 percent by weight. In certain embodiments, the leached glassfibers contain at least 90 percent by weight silica, and in certain ofthese, from about 90 percent by weight to less than about 99 percent byweight silica. The fibers are also substantially shot free and exert aminimum holding pressure for holding said fragile structure within saidhousing of one of (i) at least about 10 kPa after 1000 cycles of testingat a hot face temperature of about 900° C., a gap bulk density of fromabout 0.3 to about 0.5 g/cm³, and a percent gap expansion of about 5percent, or (ii) at least about 50 kPa after 1000 cycles of testing at ahot face temperature of about 300° C., a gap bulk density of from about0.3 to about 0.5 g/cm³, and a percent gap expansion of about 2 percent.

The average fiber diameter of these leached glass fibers may be greaterthan at least about 3.5 microns, and often greater than at least about 5microns. On average, the glass fibers typically have a diameter of about9 microns, up to about 14 microns. Thus, these leached glass fibers arenon-respirable.

Examples of leached glass fibers high in silica content and suitable foruse in the production of a flexible fibrous material layer for acatalytic converter or other known gas-treating device include thoseleached glass fibers available from BelChem Fiber Materials GmbH,Germany, under the trademark BELCOTEX and from Hitco Carbon Composites,Inc. of Gardena Calif., under the registered trademark REFRASIL, andfrom Polotsk-Steklovolokno, Republic of Belarus, under the designationPS-23(R).

The BELCOTEX fibers are standard type, staple fiber pre-yarns. Thesefibers have an average fineness of about 550 tex and are generally madefrom silicic acid modified by alumina. The BELCOTEX fibers are amorphousand generally contain about 94.5 silica, about 4.5 percent alumina, lessthan 0.5 percent sodium oxide, and less than 0.5 percent of othercomponents. These fibers have an average fiber diameter of about 9microns and a melting point in the range of 1500° to 1550° C. Thesefibers are heat resistant to temperatures of up to 1100° C., and aretypically shot free.

The REFRASIL fibers, like the BELCOTEX fibers, are amorphous leachedglass fibers high in silica content for providing thermal insulation forapplications in the 1000° to 1100° C. temperature range. These fibersare between about 6 and about 13 microns in diameter, and have a meltingpoint of about 1700° C. The fibers, after leaching, typically have asilica content of about 95 percent by weight. Alumina may be present inan amount of about 4 percent by weight with other components beingpresent in an amount of 1 percent or less.

The PS-23 (R) fibers from Polotsk-Steklovolokno are amorphous glassfibers high in silica content and are suitable for thermal insulationfor applications requiring resistance to at least about 1000° C. Thesefibers have a fiber length in the range of about 5 to about 20 mm and afiber diameter of about 9 microns. These fibers, like the REFRASILfibers, have a melting point of about 1700° C.

By further treating either the leached glass fibers prior to formationof the flexible fibrous material layer, or flexible fibrous materiallayers made from these fibers after formation, the holding pressureperformance of the flexible fibrous material layer can be improvedsufficiently, even after cycling, to be adaptable for use in an exhaustgas treatment device. In one particular embodiment, these leached glassfibers (or the mounting mats containing them) may be heat treated attemperatures ranging from above at least about 900° C., such as fromabout 900° C. to about 1100° C., such that the mounting mat employingthese fibers may exert the minimum required holding pressure within theexhaust gas treatment device, even after 1000 cycles of expansion andcontraction.

The flexible fibrous material layer of this embodiment may include up to100 percent by weight of the leached and surface treated glass fiberscontaining silica. However, in other embodiments, the flexible fibrousmaterial layer may optionally comprise other known fibers such asalumina/silica fibers, or other ceramic or glass fibers suitable for usein the production of mounting mats for the particular temperatureapplications desired. Thus, alumina/silica fibers such as refractoryceramic fibers may be optionally employed for high temperature or wideranging temperature applications. Other ceramic or glass fibers such asS-glass may be used with the leached glass silica fibers in similar orlower temperature applications. In such instances, however, the flexiblefibrous material layer preferably includes at least 50 percent by weightof leached and surface treated glass fibers containing silica. In otherwords, the majority of the fiber utilized in the production of the matwill be leached and surface treated glass fibers containing silica, andin certain embodiments, at least 80 percent by weight of the fibers willbe leached and surface treated glass fibers containing silica.

In certain alternative embodiments, fibers such as S2-glass and the likemay be added to the flexible fibrous material layer in quantities offrom greater than 0 to about 50 percent by weight, based upon 100percent by weight of the total mat. In other alternative embodiments,the flexible fibrous material layer may include refractory ceramicfibers in addition to the leached glass fibers. When refractory ceramicfibers, that is, alumina/silica fibers or the like are utilized, theymay be present in an amount ranging from greater than 0 to less thanabout 50 percent by weight, based upon 100 percent by weight of thetotal flexible fibrous material layer.

The flexible fibrous material layer may or may not include a binder.Either a single type of binder or mixture of more than one type ofbinder may be included within the flexible fibrous material layer.Suitable binders include organic binders, inorganic binders and mixturesof these two types of binders. According to certain embodiments, theintumescent or non-intumescent flexible fibrous material layer, includeone or more organic binders. The organic binders may be provided as asolid, a liquid, a solution, a dispersion, a latex, or similar form. Theorganic binder may comprise a thermoplastic or thermoset binder, whichafter cure is a flexible material that can be burned out of an installedmounting mat. Examples of suitable organic binders include, but are notlimited to, acrylic latex, (meth)acrylic latex, copolymers of styreneand butadiene, vinylpyridine, acrylonitrile, copolymers of acrylonitrileand styrene, vinyl chloride, polyurethane, copolymers of vinyl acetateand ethylene, polyamides, silicones, and the like. Other resins includelow temperature, flexible thermosetting resins such as unsaturatedpolyesters, epoxy resins and polyvinyl esters.

The organic binder may be included in the mounting mat in an amount ofgreater than 0 to about 20 weight percent, from about 0.5 to about 15weight percent, from about 1 to about 10 weight percent, or from about 2to about 8 weight percent, based on the total weight of the flexiblefibrous material layer.

The flexible fibrous material layer may include polymeric binder fibersinstead of, or in combination with, the resinous or liquid binder. Thesepolymeric binder fibers may be used in amounts ranging from greater than0 to about 20 percent by weight, from about 1 to about 15 weightpercent, and from about 2 to about 10 weight percent, based upon 100percent by weight of the total composition, to aid in binding the heattreated fibers together. Suitable examples of binder fibers includepolyvinyl alcohol fibers, polyolefin fibers such as polyethylene andpolypropylene, acrylic fibers, polyester fibers, ethyl vinyl acetatefibers, nylon fibers and combinations thereof.

When an organic binder is used, the components are mixed to form amixture or slurry. The slurry of fibers and binder is then formed into aflexible fibrous material layer structure and the binder is removed,thereby providing a flexible fibrous material layer containing theheat-treated silica fibers (and optionally additional fibers).Typically, a sacrificial binder is employed to initially bond the fiberstogether. By “sacrificial,” it is meant that the organic binder willeventually be burned out of the flexible fibrous material layer, leavingonly the heat treated silica fibers (and other ceramic or glass fibers,if used) as the flexible fibrous material layer.

In addition to organic binders, the flexible fibrous material layer mayalso include inorganic binder material. Without limitation, suitableinorganic binder materials include inorganic particulate materials,colloidal dispersions of alumina, silica, zirconia, and mixturesthereof.

The flexible fibrous material layer may be prepared by any knowntechniques commonly used in the preparation of flexible fibrous materiallayer. For example, using a papermaking process, the fibers may be mixedwith a binder or other binder fibers to form a mixture or slurry. Thefibrous components may be mixed at about a 0.25% to 5% consistency orsolids content (0.25-5 parts solids to 99.75-95 parts water). The slurrymay then be diluted with water to enhance formation, and it may finallybe flocculated with a flocculating agent and drainage retention aidchemicals. The flocculated mixture or slurry may be placed onto apapermaking machine to be formed into a ply or sheet of fiber containingpaper. Alternatively, the plies or sheets may be formed by vacuumcasting the slurry. In either case, the plies or sheets are typicallydried in ovens. For a more detailed description of standard papermakingtechniques employed, see U.S. Pat. No. 3,458,329, the disclosure ofwhich is incorporated herein by reference.

In other embodiments, the fibers may be processed into a flexiblefibrous material layer by conventional means such as dry air laying. Theflexible fibrous material layer at this stage has very little structuralintegrity and is very thick relative to conventional catalytic converterand diesel trap mounting mats. The resultant flexible fibrous materiallayer can therefore be dry needled, as is commonly known in the art, todensify the flexible fibrous material layer and increase its strength.Heat treatment of certain fibers may occur prior to formation of the mator after the flexible fibrous material layer is needled.

Where the dry air layering technique is used, the flexible fibrousmaterial layer may be alternatively processed by the addition of abinder to the flexible fibrous material layer by impregnation to form afiber composite. In this technique, the binder is added after formationof the flexible fibrous material layer, rather than forming the flexiblefibrous material layer prepreg as noted hereinabove with respect to theconventional papermaking technique. This method of preparing theflexible fibrous material layer aids in maintaining fiber length byreducing breakage. It will be appreciated, however, that heat treatment,may occur prior to addition of any binder.

Methods of impregnation of the flexible fibrous material layer with thebinder include complete submersion of the flexible fibrous materiallayer in a liquid binder system, or alternatively brushing, coating,dipping, rolling, splashing, or spraying the mat. In a continuousprocedure, a flexible fibrous material layer which can be transported inroll form, is unwound and moved, such as on a conveyer or scrim, pastspray nozzles which apply the binder to the flexible fibrous materiallayer. Alternatively, the mat can be gravity-fed past the spray nozzles.The mat/binder prepreg is then passed between press rolls, which removeexcess liquid and densify the prepreg to approximately its desiredthickness. The densified prepreg may then be passed through an oven toremove any remaining solvent and if necessary to partially cure thebinder to form a composite. The drying and curing temperature isprimarily dependent upon the binder and solvent (if any) used. Thecomposite can then either be cut or rolled for storage ortransportation.

The flexible fibrous material layer can also be made in a batch mode, byimmersing a section of the mat in a liquid binder, removing the prepregand pressing to remove excess liquid, thereafter drying to form thecomposite and storing or cutting to size.

It is noted that flexible fibrous material layer produced from thesefibers may be too low in density for easy use in certain catalyticconverter applications. Therefore, they may undergo furtherdensification by any manner known in the art to provide a higherdensity. One such manner of densification is to needle punch the fibersso as to intertwine and entangle them. Additionally or alternatively,hydro-entangling methods may be used. Another alternative is to pressthe fibers into a flexible fibrous material layer form by rolling themthrough press rollers. Any of these methods of densification of theflexible fibrous material layer or a combination of these methods can bereadily used to obtain a mounting mat of the desired form.

Regardless of which of the above-described techniques are employed, theflexible fibrous material layer may be cut, such as by die stamping, toform mounting mats of exact shapes and sizes with reproducibletolerances. The flexible fibrous material layer exhibits suitablehandling properties upon densification as by needling or the like,meaning it can be easily handled and is not so brittle as to crumble inone's hand like many other fiber blankets or mats. It can be easily andflexibly fitted or wrapped around the catalyst support structure or likefragile structure without cracking, and then disposed within thecatalytic converter housing. In certain embodiments, melt-formed,leached glass fibers high in silica content are subjected to a surfacetreatment, which results in an increase in the holding pressureperformance of the flexible fibrous material layer containing aplurality of the leached, high silica containing glass fibers.

According to one embodiment, the exterior surfaces of the fibers may betreated by applying an inorganic particulate material to at leastportions of the fiber surfaces. Useful inorganic particulate materialsthat may be utilized to treat the exterior of the fiber surfaces of theleached glass fibers include, without limitation, colloidal dispersionsof alumina, silica, zirconia, and mixtures thereof According to oneembodiment, the inorganic material used to treat the exterior surfacesof the leached glass fibers, thereby increasing the overall holdingpressure performance of the mounting mat, is a colloidal dispersion ofalumina.

At least a portion of the exterior surfaces of at least a portion of thefibers of the flexible fibrous material layer may include a continuousor discontinuous coating of colloidal alumina, silica, zirconia, andmixtures thereof The colloidal oxide may be applied to the exteriorsurfaces of the fibers by any suitable means, without limitation, bycoating, dipping, spraying, splashing, and the like. The colloidal oxidemay be applied to the exterior surfaces of the fibers in either acontinuous or discontinuous pattern. Moreover, the process of applyingthe colloidal oxide to the exterior surfaces of the fibers may becarried out during or after manufacture of the glass fibers.

The flexible fibrous material layer may comprise only one or moreintumescent fibrous mats, or only one or more non-intumescent fibrousmats, as well as combinations of at least one intumescent and at leastone non-intumescent mat or layer within a hybrid mat.

Additionally, separate flexible fibrous material layer may contacteither surface of the microporous insulation layer, such as, by way ofexample but not limitation at least one intumescent mat proximate to thesubstrate and at least one non-intumescent mat proximate to the housing.

As an exhaust gas treatment device cycles from ambient temperature tooperating temperature, the components comprising the device reach theirindividual operating temperatures. The operating temperature for anygiven component in the exhaust gas treatment device may be less than theoperating temperature for the device itself, because some components areinsulated from higher temperature components. As components heat, theywill expand in proportion to their thermal expansion coefficients.

This expansion produces a change in the strain state of the component.Because all components will not experience identical thermal strain,thermal strain causes component interference forces to change. That is,a change in the strain state of the component causes a correspondingchange in the stress state of the component, and a resultant change inthe forces between it and other components with which it is engaged.

In certain embodiments, the insulating layer is disposed to engage thesubstrate directly, a flexible fibrous material layer is disposed overthe insulating layer and engages it directly, and a housing is disposedover the mounting mat and engages it directly. In other embodiments, theflexible fibrous material layer is disposed to engage the substratedirectly, an insulating layer is disposed over the flexible fibrousmaterial layer and engages it directly, and a housing is disposed overthe insulating layer and engages it directly.

In embodiments in which an insulation layer is positioned between thesubstrate and the flexible fibrous material layer, the insulation layerinsulates the flexible fibrous material layer, and all other componentsinstalled on the cold side of the insulating layer (cold sidecomponents), from the substrate and heat flowing from the substrate, andthereby promotes lower operating temperatures for the flexible fibrousmaterial layer and other cold side components than the operatingtemperature of the substrate.

Because ambient temperature is lower than the operating temperature ofthe flexible fibrous material layer, promotion of lower flexible fibrousmaterial layer operating temperature and other cold side componentsoperating temperatures decreases both the amplitude of temperaturechange and the maximum temperature experienced by the flexible fibrousmaterial layer and other cold side components during any givenoperational cycle. The decrease in the amplitude of temperature changeresults in a corresponding decrease in the amplitude of the change inthermal strain of the mounting mat and other cold side components.Because a change in the strain state of the component causes acorresponding change in the stress state of the component, and aresultant change in the forces between it and other components withwhich it is engaged, decreasing the amplitude of the change in thermalstrain of a component results in a decrease in the change in the forcesbetween it and other components with which it is engaged.

The substrate is held in place by mounting forces developed fromcompression by other components. These mounting forces are subject to anupper and lower design limit. The upper limit is the force required tocause damage to the substrate; the mounting forces are not sufficient toharm the substrate. The lower limit is the maximum displacement forcewhich the substrate will experience in service; the mounting forces areat least sufficient to hold the substrate in place against alldisplacement forces experienced in service. As noted above, thermalstrain can cause the actual mounting forces developed during the courseof operation to fluctuate. By insulating the components which developthe mounting forces, the amplitude of the change in thermal strain ofthe components is decreased as is the amplitude of the change in themounting forces between them and the substrate. By decreasing theamplitude of the change in the mounting forces between other componentsand the substrate, maintaining the mounting forces within their designlimits is simplified.

In embodiments in which the flexible fibrous material layer ispositioned between the substrate and the insulation layer, theinsulation layer insulates the flexible fibrous material layer from theambient environment and permits higher mounting mat operatingtemperatures than the alternative. In certain embodiments, the flexiblefibrous material layer additionally comprises intumescent materials. Inthose embodiments in which the flexible fibrous material layer comprisesintumescent materials, the positioning of the flexible fibrous materiallayer between the substrate and the insulation layer permits flexiblefibrous material layer operating temperatures high enough to induce theintumescent response in the intumescent materials.

In certain embodiments, the multiple layer mounting system may be usedas end cone insulation in an exhaust gas treatment device. According tocertain embodiments, an end cone for an exhaust gas treatment device isprovided. The end cone generally comprises an outer metallic cone, aninner metallic cone and end cone insulation that is disposed within thegap or space between the outer and inner metallic end cones.

According to other embodiments, the end cone may comprise an outermetallic cone and at least one layer of cone insulation that ispositioned adjacent to the inner surface of the outer metallic cone.According to these embodiments, the end cone assembly is not providedwith an inner metallic cone. Rather, the cone insulation is rigidized insome manner to provide a self-supporting cone structure that isresistant to the high temperature gases flowing through the device.

An exhaust gas treatment device including at least one end cone isprovided. The exhaust gas treatment device comprises a housing, afragile structure positioned within the housing, an inlet and an outletend cone assemblies for attaching exhaust pipes to the housing, each endcone assembly comprising an inner end cone housing and an outer end conehousing; and end cone insulation comprising the multiple layer mountingsystem described in the various embodiments discussed herein.

FIG. 1 shows a first illustrative embodiment of a multiple layer mat 10.Mounting mat 10 comprises a first layer 12 comprising a non-intumescentsheet of inorganic fibers having a first major surface 14 and a secondmajor surface 16 opposite the first major surface. Mat 10 includes asecond layer 18 comprising a non-intumescent sheet of inorganic fibershaving a first major surface 20 and a second major surface 22 oppositethe first major surface 20. A microporous inorganic insulating layer 24is positioned between said first non-intumescent layer 12 and secondnon-intumescent layer 18.

FIG. 2 shows a multiple layer mat 30 comprising a first layer 32comprising an intumescent sheet of inorganic fibers having a first majorsurface 34 and a second major surface 36 opposite the first majorsurface 34. Mat 30 also includes a second layer 38 comprising anintumescent sheet of inorganic fibers having a first major surface 40and a second major surface 42 opposite the first major surface 40. Amicroporous inorganic insulating layer 44 is positioned between saidfirst intumescent layer 32 and second intumescent layer 38.

FIG. 3 shows a multiple layer mat 50 comprising a first layer 52comprising a non-intumescent sheet of inorganic fibers having a firstmajor surface 54 and a second major surface 56 opposite the first majorsurface 54. A second layer 58 comprising a microporous inorganicinsulating layer having a first major surface 60 and a second majorsurface 62 opposite the first major surface 60 is positioned in adjacentcontact with said first layer 52. A bonding means 64 is located betweensaid first layer 52 and said second layer 58.

FIG. 4 shows a multiple layer mat 70 that has a first layer 72comprising a non-intumescent sheet of inorganic fibers having a firstmajor surface 74 and a second major surface 76 opposite the first majorsurface 74. A second layer 78 comprising a microporous inorganicinsulating layer having a first major surface 80 and a second majorsurface 82 opposite the first major surface 80 is placed adjacent thefirst layer 72. A banding means 84 encircles the first 72 and second 78layers to hold them in adjacent contact. According to the embodimentshown in FIG. 4, adhesive tape 86 is used to join opposite ends of thebanding material 84.

FIG. 5 shows a multiple layer mat 90 comprising a first layer 92comprising a non-intumescent sheet of inorganic fibers having a firstmajor surface 94 and a second major surface 93 opposite the first majorsurface 94. A second layer 96 comprising a microporous inorganicinsulating layer having a first major surface 98 and a second majorsurface 100 opposite the first major surface 98. The first 92 and second96 layers are brought into adjacent contact and are encapsulated withina common polymeric bag 102.

FIG. 6 shows a multiple layer mat 110 comprising a first layer 112comprising a non-intumescent sheet of inorganic fibers having a firstmajor surface 114 and a second major surface 116 opposite the firstmajor surface 114. A scrim layer 118 having a first major surface 120and a second major surface 122 opposite the first major surface 120 isbrought into adjacent contact with one of the first or second majorsurfaces of layer 112. A microporous inorganic insulating layer 124 ispositioned between the first non-intumescent layer 112 and said scrimlayer 118.

FIG. 7 shows a multiple layer support 130 comprising a microporousinorganic insulating layer comprising a three-dimensional pre-form 132.A flexible layer 134 of a fibrous or intumescent mat material is wrappedabout at least a portion of the perimeter of said pre-form 132.

FIG. 8 shows a multiple layer support 140 comprising a three-dimensionalpre-form comprising an inner layer 142 of microporous inorganicinsulating material and an outer layer 144 applied over at least aportion of said inner layer 142.

One illustrative configuration of an exhaust gas treatment device isshown as a catalytic converter, generally designated by the numeral 150in FIG. 9. It should be understood that the exhaust gas treatment deviceis not limited to use in the catalytic converter shown in illustrativeFIG. 9, and so the configuration is shown only to exemplify the device.In fact, the mounting mat may be used to mount or support any fragilestructure suitable for treating exhaust gases, such as a diesel catalyststructure, a diesel particulate filter, or the like. Catalytic converter150 may include a generally tubular housing 152, typically formed of twopieces of metal, e.g. high temperature-resistant steel, held together byflange 154. Housing 152 includes an inlet 156 at one end and an outlet(not shown) at its opposite end. The inlet 156 and outlet are suitablyformed at their outer ends whereby they may be secured to conduits inthe exhaust system of an internal combustion engine.

Device 150 contains a catalyst support structure, such as a frangibleceramic monolith substrate 160, which is supported and restrained withinhousing 152 by the hybrid substrate mounting system 170 having at leastone layer of microporous insulation 172 and a second layer 174.

EXAMPLES

Two mounting mats were created according to the procedures and processesdescribed above. The comparative mounting mat comprised anon-intumescent mat, while a subject mounting mat comprised anon-intumescent layer substantially similar to the non-intumescent matof the comparative mounting mat, additionally comprising a layer ofmicroporous inorganic insulation comprising microporous silica.

Both the comparative and subject mounting mats were placed intosubstantially identical catalytic converters. A thermocouple was spotwelded onto the shell of each catalytic converter. The substrates ofeach catalytic converter were electrically wired and heated to atemperature of 750° C. over a period of 20 minutes. The substrates werethen maintained at a temperature of 750° C. for a period of 30 minutes,and the temperature of the shells was recorded. The substrates were thenfurther heated to a temperature of 1,000° C. over a period of 20minutes, which temperature was maintained for an additional 30 minutes,after which the temperature of the shells was again recorded. Theresults are shown in TABLE II.

TABLE II Shell Temp. at 750° C. Shell Temp. at 1,000° C. Substrate Temp.Substrate Temp. Comparative Mat 358° C. 460° C. Subject Mat 316° C. 376°C. Percent Reduction 12% 18% in Temp.

A reduction of the temperature of the shell by 42° C. at a substratetemperature of 750° C. and by 84° C. at a substrate temperature of1,000° C. represent 12% and 18% increases in insulative efficiency,respectively. The results show that the subject mat reduces thetemperature of the shell as compared to the comparative, conventionalmounting mat. Further, the insulative efficiency increases at highersubstrate temperatures.

While the system has been described in connection with variousembodiments, as shown in the various figures, it is to be understoodthat other similar embodiments may be used or modifications andadditions may be made to the described embodiments for performing thesame function. Furthermore, the various illustrative embodiments may becombined to produce the desired results. Therefore, the substratemounting system and exhaust gas treatment device should not be limitedto any single embodiment, but rather construed in breadth and scope inaccordance with the recitation of the appended claims.

The invention claimed is:
 1. A multiple layer mat comprising: a first layer comprising a sheet of inorganic fibers having a first major surface and a second major surface opposite the first major surface; a second layer comprising a sheet of inorganic fibers having a first major surface and a second major surface opposite the first major surface; a microporous inorganic insulating layer positioned between the first layer and the second layer.
 2. The multiple layer mat of claim 1, wherein both of the first layer and the second layer are non-intumescent.
 3. The multiple layer mat of claim 1, wherein both of the first layer and the second layer are intumescent.
 4. The multiple layer mat of claim 1, wherein the first layer is either non-intumescent or intumescent and, if the first layer is intumescent then the second layer is non-intumescent, or if the first layer is non-intumescent then the second layer is intumescent.
 5. The multiple layer mat of claim 1, wherein the inorganic fibers are selected from the group consisting of high alumina polycrystalline fibers, ceramic fibers, refractory ceramic fibers, mullite fibers, glass fibers, biosoluble fibers, quartz fibers, silica fibers, and combinations thereof.
 6. The multiple layer mat of claim 5, wherein the high alumina polycrystalline fibers comprise the fiberization product of about 72 to about 100 weight percent alumina and about 0 to about 28 weight percent silica.
 7. The multiple layer mat of claim 5, wherein the ceramic fibers comprise alumino-silicate fibers comprising the fiberization product of about 45 to about 72 weight percent alumina and about 28 to about 55 weight percent silica.
 8. The multiple layer mat of claim 5, wherein the biosoluble fibers comprise magnesia-silica fibers comprising the fiberization product of about 65 to about 86 weight percent silica, from about 14 to about 35 weight percent magnesia and about 5 weight percent of less impurities.
 9. The multiple layer mat of claim 5, wherein the biosoluble fibers comprise calcia-magnesia-silica fibers comprising the fiberization product of about 45 to about 90 weight percent silica, greater than 0 to about 45 weight percent calcia, and greater than 0 to about 35 weight percent magnesia.
 10. The multiple layer mat of claim 9, wherein the calcia-magnesia-silica fibers comprise the fiberization product of about 60 to about 70 weight percent silica, from about 16 to about 35 weight percent calcia, and from about 2 to about 19 weight percent magnesia.
 11. An exhaust gas treatment device comprising: a housing; a fragile structure located within the housing; and the multiple layer mat of claim 1 disposed between the housing and the fragile structure.
 12. An end cone for an exhaust gas treatment device comprising: an outer metallic cone; an inner metallic cone; and cone insulation disposed between said outer and inner metallic end cones, said cone insulation comprising the multiple layer mat of claim
 1. 13. An end cone for an exhaust gas treatment device comprising: an outer metallic cone; and self-supporting cone insulation comprising the multiple layer mat of claim 1 disposed adjacent the inner surface of said outer metallic end cone.
 14. A multiple layer mat comprising: a first layer comprising a sheet of inorganic fibers having a first major surface and a second major surface opposite the first major surface; a second layer adjacent said first layer, said second layer comprising a microporous inorganic insulating layer having a first major surface and a second major surface opposite the first major surface; and wherein the first layer and the second layer are encapsulated within a polymeric bag.
 15. The multiple layer mat of claim 14, wherein the first layer is non-intumescent.
 16. The multiple layer mat of claim 14, wherein the first layer is intumescent.
 17. The multiple layer mat of claim 14, wherein the inorganic fibers are selected from the group consisting of high alumina polycrystalline fibers, ceramic fibers, mullite fibers, glass fibers, biosoluble fibers, quartz fibers, silica fibers, and combinations thereof.
 18. The multiple layer mat of claim 14, wherein the polymeric bag is shrink wrapped around the first layer and the second layer.
 19. The multiple layer mat of claim 14, wherein the polymeric bag comprises a polyethylene polymer.
 20. An exhaust gas treatment device comprising: a housing; a fragile structure located within the housing; the multiple layer mat of claim 14 disposed between the housing and the fragile structure.
 21. An end cone for an exhaust gas treatment device comprising: an outer metallic cone; an inner metallic cone; and cone insulation disposed between said outer and inner metallic end cones, said cone insulation comprising the multiple layer mat of claim
 14. 22. An end cone for an exhaust gas treatment device comprising: an outer metallic cone; and self-supporting cone insulation comprising the multiple layer mat of claim 14 disposed adjacent the inner surface of said outer metallic end cone.
 23. A multiple layer support comprising: a microporous inorganic insulating layer comprising a three-dimensional pre-form; and a flexible fibrous layer disposed about at least a portion of the perimeter of the three-dimensional pre-form.
 24. The multiple layer support of claim 23, wherein the flexible fibrous layer comprises a sheet of inorganic fibers.
 25. The multiple layer support of claim 24, wherein the flexible fibrous layer is non-intumescent.
 26. The multiple layer support of claim 24, wherein the flexible fibrous layer is intumescent.
 27. The multiple layer support of claim 23, wherein the inorganic fibers are selected from the group consisting of high alumina polycrystalline fibers, ceramic fibers, mullite fibers, glass fibers, biosoluble fibers, quartz fibers, silica fibers, and combinations thereof.
 28. The multiple layer support of claim 23, wherein the flexible layer is placed on the at least a portion of the three-dimensional pre-form prior to pre-forming the three-dimensional pre-form.
 29. An exhaust gas treatment device comprising: a housing; a fragile structure located within the housing; and the multiple layer support of claim 23 disposed between the housing and the fragile structure.
 30. An end cone for an exhaust gas treatment device comprising: an outer metallic cone; an inner metallic cone; and cone insulation disposed between said outer and inner metallic end cones, said cone insulation comprising the multiple layer support of claim
 23. 31. An end cone for an exhaust gas treatment device comprising: an outer metallic cone; and self-supporting cone insulation comprising the multiple layer support of claim 23 disposed adjacent the inner surface of said outer metallic end cone.
 32. A multiple layer mat comprising: a first layer comprising a sheet of inorganic fibers having a first major surface and a second major surface opposite the first major surface; a second layer comprising a microporous inorganic insulating layer having a first major surface and a second major surface opposite the first major surface; and either: (i) a bonding means between the first layer and the second layer; (ii) a banding means encircling at least a portion of the exterior surfaces of the first layer and the second layer, such that the first layer is engaged with the second layer; or (iii) a scrim layer, wherein the second major surface of the first layer is engaged with the first major surface of the second layer, and the scrim layer is engaged with the second major surface of the second layer.
 33. The multiple layer mat of claim 32, wherein the first layer is non-intumescent.
 34. The multiple layer mat of claim 32, wherein the first layer is intumescent.
 35. The multiple layer mat of claim 32, wherein the inorganic fibers are selected from the group consisting of high alumina polycrystalline fibers, ceramic fibers, mullite fibers, glass fibers, biosoluble fibers, quartz fibers, silica fibers, and combinations thereof.
 36. The multiple layer mat of claim 32, wherein the bonding means comprises an adhesive.
 37. The multiple layer mat of claim 32, wherein the banding means comprises a tourniquet.
 38. The multiple layer mat of claim 32, wherein the scrim is at least one of tea bags, aluminum foil, ethylene, or paper.
 39. An exhaust gas treatment device comprising: a housing; a fragile structure located within the housing; the multiple layer mat of claim 32 disposed between the housing and the fragile structure.
 40. An end cone for an exhaust gas treatment device comprising: an outer metallic cone; an inner metallic cone; and cone insulation disposed between said outer and inner metallic end cones, said cone insulation comprising the multiple layer mat of claim
 32. 41. An end cone for an exhaust gas treatment device comprising: an outer metallic cone; and self-supporting cone insulation comprising the multiple layer mat of claim 32 disposed adjacent the inner surface of said outer metallic end cone. 